This invention relates to an apparatus for gripping tubular members and, in particular, pipes in the oil well industry. More specifically, it relates to an interchangeable faceplate to be placed on a jaw carrier whereby the faceplate serves to engage reliably with pipe.
In the oil and gas industry, in order to grip drill pipe it is necessary to apply high gripping forces while simultaneously rotating the pipe or restraining the pipe against rotation. Typically, such forces are now applied to pipe through the use of power tongs or a back-up tong. Within a power tong, a jaw assembly is rotatably mounted with provision for jaw surfaces within the assembly to receive and embrace the pipe once torque is to be applied. A back-up tong has similar jaw surfaces.
It is normal to use gripping plates which are inserted into the jaw assembly as the actual component that contacts with the pipe. These plates or die inserts are typically made of hardened metal and/or carry a gripping, eg. textured, surface which is suited for developing a high, frictional contact with the surface of pipe. They may also have smooth surfaces formed on softer metal. Such die inserts are installed within a jaw assembly at the focal point for the forces which are to be applied to pipe. Those forces include a rotational torque intended to turn the pipe in order to make or break pipe joints or carry-out rotation for drilling; a compressional force caused by the camming surface of the rotary gear forcing the jaw assembly to press up against the pipe, and vertical forces arising, as for example, when the weight of a power tong rests upon, or is dropped onto, the pipe.
As such jaw plates are subject to wear, they must be readily replaceable within the jaw assembly. Various systems for attaching jaw plates within a jaw assembly have been proposed. In particular, U.S. Pat. Nos. 4,576,067; 5,911,796 and 6,253,643 all to Buck describe a removable die plate which is provided with an external, convex surface having splines which run vertically. These splines mate with complementary grooves formed in the body of the jaw assembly. The splines serve to provide the necessary torque transfer between the jaw assembly and the jaw plates, serving to hold the die plate in place while rotating forces are applied to the pipe.
In U.S. Pat. No. 4,576,067 the die is held vertically in place by conventional means such as a screw that engages with a lip protruding from the convex surface of the die plate. While the splines of this prior invention provides a much greater and more robust surface area between the jaw assembly and the die plate to transfer rotational forces, the screw and lip arrangement makes little provision to absorb vertical forces that may arise when a section of pipe is lowered or raised vertically, carrying the power tong with it. The vertical forces arising under oil field conditions may be substantial. In the referenced U.S. patent above the only provision to accommodate such forces is the screw and lip feature as described. Depending on the dimensions of these components the lip and screw feature may be inadequate to support substantial vertical loads.
In U.S. Pat. 6,253,643 upper and lower lips or edges are provided to contain the jaw plate. These lips are emoveably attached to the jaw assembly by fasteners. To more securely absorb vertical loads arising between the jaw plate and jaw assembly, a curved insert is fitted into a keyway provided by opposed annular slots formed in the jaw plate and jaw assembly splined surfaces. Thus installation of this jaw plate also requires manipulation of an insert.
In the case of prior art designs the splines are cut with gear-like orientations. Consequently, the die plate must normally be slid into place. The die plate in these disclosures may not readily fit directly in place by a faceon-face insertion procedure due to the angles of the outer splines and grooves along the die plate edges.
It is an object of this invention to provide an improved form of die plate that is adapted to better transfer vertical forces between the die plate and the jaw assembly to which it is mounted and is more easily fitted into place. It is a further object of this invention to provide improved means for restraining a die plate against vertically-applied forces.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims, which conclude this Specification.
According to the invention in one aspect, a jaw assembly for gripping tubular members is provided which includes a concave seating surface within a jaw plate carrier portion of the jaw assembly, such concave seating surface having a plurality of parallel vertical grooves arcuately spaced on said concave surface, and a plurality of parallel, circular, horizontal grooves spanning said concave surface, preferably substantially from side to side. These grooves respectively define straight vertical and curved horizontal splines or spline segments. Spline segments arise from splines that are interrupted by gaps as further described below. Splines and spline segments qualify as spline means.
This concave seating surface mates with a jaw plate having a convex surface with a complementary array of vertically and horizontally aligned protrusions that are positioned and dimensioned to engage with portions of the vertical and horizontal grooves of the jaw plate carrier portion, there being slots between such protrusions to intimately receive the splines and/or spline segments on the jaw plate carrier portion of the jaw assembly to thereby ensure the effective transfer of forces there between.
The pattern of the vertical and horizontal grooves and corresponding protrusions, is flexible. The horizontal grooves maybe bounded by the vertical grooves, above and below the horizontal grooves. Or the vertical grooves may be bounded by the horizontal grooves above and below the vertical grooves. And these respective grooves may be interspersed in any manner that provides satisfactory coupling between the jaw plate and the jaw plate carrier portion of the jaw assembly.
According to another aspect of the invention, the fit between the jaw plate and jaw plate carrier portion allows the jaw plate to be radially pressed into position by radial advancement of the jaw plate into the concave seating surface.
By a further aspect of the invention the horizontal splines may be interrupted by gaps that are aligned with the vertical grooves so as to allow a vertical sliding insertion of a die plate having strictly vertical splines and grooves on its convex surface. Such gaps convert the horizontal splines into spline segments. In such case, a radiably-insertable jaw plate according to the invention may mate with the jaw carrier seating surface with portions of the protrusions of the jaw plate extending into the horizontal grooves of the seating surface, in vertical alignment with the spline segments present on such seating surface. An advantage of providing a seating surface of this design is that such a seating surface may receive jaw plates having strictly vertically aligned slots and protrusions as well as jaw plates with dual types of protrusions, according to the invention.
The objective of providing an engagement surface between the jaw plate and the jaw carrier assembly as described is to enhance the capacity of the interface between these components to transmit not only a rotary torque to a pipe, but also to absorb vertical loads as well.
As described, a jaw plate, may be installed on the jaw plate carrier portion of a jaw assembly by being pressed radially in place.
The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.